Here's the funny thing - now that I swapped in a 4L60, my MPGs went from about 12.5 (old 3-spd) down to 9.5 (4L60). Then last week I had a trailer with a heavy load, and stayed out of OD. My average jumped UP to over 10.5.
So I installed a tach. My current RPM are 1900 @ 65. And that is the spot where my MPGs s-u-c-k.
So this tank I am going to drive around without using OD at all. We'll see what happens to the MPGs. My guess is that they will jump up, and if so then I will need to swap out differential gears.
Using
a calculator online It seems like my diff gears are possibly 3.73... I don't know what they are. But I have 29.1" tires, and using 3.73 as the gears, it comes in about right.
So if it happens like I think it will, I'll need to figure out what gears to swap to.